Answer :
x - blue pens
[tex]\dfrac{21}{x}=\dfrac{3}{1}\\ 3x=21\\ x=7\\\\ 21+7=28[/tex]
28 in total
[tex]\dfrac{21}{x}=\dfrac{3}{1}\\ 3x=21\\ x=7\\\\ 21+7=28[/tex]
28 in total